1 Field of the Invention
The present invention relates to a vapor device and method for drying articles such as semiconductor wafers with substances such as isopropyl alcohol. The invention may also be used to cleanse and rinse the articles prior to drying.
2 Description of the Related Art
The process for manufacturing semiconductor wafers made of materials such as silicon typically requires a chemical treatment step followed by the steps of rinsing and drying the wafers. In related art devices and methods, after the wafers are rinsed with deionized water, they are placed on a movable transport elevator and lowered into a vapor drying tank. The vapor drying tank, which may be made of quartz, includes a deep lower pan for holding a volatile drying liquid such as isopropyl alcohol (IPA). The wafers are lowered to a position above the pan, and the IPA in the pan is heated to its boiling point. Heating causes the IPA to vaporize, and vaporized IPA is absorbed by the cool deionized water on the wafer surfaces. As this liquefying process continues, the deionized water loses its surface tension and shears off of the wafer surfaces. Ultimately, all moisture adhering to the wafers is displaced with IPA. The remaining IPA quickly evaporates providing moisture-free wafer surfaces.
After a predetermined time, the movable transport elevator raises the wafer from the tank. Typically, some IPA remains on the wafer surfaces in a molecular thickness. This requires that the wafers be dried for an additional period of time in nitrogen or ambient air.
There are a number of drawbacks with the above-mentioned related art devices and methods. First, the deionized water displaced from the wafer and wafer carrier as well as the absorption of water moisture in the atmosphere causes a gradual increase in the water moisture concentration of the IPA. As the moisture concentration of the IPA increases, the wafer-drying performance of the system decreases.
Another drawback of the related art devices and methods is a susceptibility to fire due to the volatility of the IPA vapor. The boiling point of IPA is 82.5.degree. C. with a flash point at ambient pressure of 22.2.degree. C. To adequately generate the necessary IPA vapor, the heaters on the tank must maintain temperatures exceeding 100.degree. C., well above the flash point of IPA. This necessitates constant monitoring and control of vapor concentrations during operation to avoid a fire or explosion.